Re: [PATCH] gpiolib: annotate struct acpi_gpio_mapping with __counted_by_ptr

[Bill Wendling]

On Sun, Sep 27, 2026 at 11:38 PM Bill Wendling <morbo@xxxxxxxxxx> wrote:
>
> The 'data' pointer field in 'struct acpi_gpio_mapping' is associated
> with the 'size' field, which represents the number of elements of
> type 'struct acpi_gpio_params' allocated for 'data'.
>
> To improve bounds checking via CONFIG_UBSAN_BOUNDS and
> CONFIG_FORTIFY_SOURCE, annotate 'data' with the __counted_by_ptr
> attribute.
>
> Analysis of allocation, assignment, and access points shows that the
> pointer is never accessed before the count is set, which guarantees that
> this annotation is safe and will not cause runtime panics or
> false-positive bounds checks.
>
> Cc: codemender-patching+linux@xxxxxxxxxx
> Assisted-by: LLM
> Signed-off-by: Bill Wendling <morbo@xxxxxxxxxx>
> ---
>  include/linux/gpio/consumer.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/gpio/consumer.h b/include/linux/gpio/consumer.h
> index fceeefd5f893..2b80cf7aa7e7 100644
> --- a/include/linux/gpio/consumer.h
> +++ b/include/linux/gpio/consumer.h
> @@ -667,7 +667,7 @@ struct acpi_gpio_params {
>
>  struct acpi_gpio_mapping {
>         const char *name;
> -       const struct acpi_gpio_params *data;
> +       const struct acpi_gpio_params *data __counted_by_ptr(size);
>         unsigned int size;
>
>  /* Ignore IoRestriction field */

There's a problem with 'drivers/firmware/efi/libstub/Makefile'. Clang
needs a compiler flag to support the "__counted_by_ptr" attribute
referencing a field *after* the pointer, like in this patch. However,
the Makefile blasts the flag away for x86 platforms. Below is a hack
that copies the part of the top-level Makefile that adds the flag. I
don't think that's a good solution. The comment in the driver's
Makefile says that the stub code executes before the kernel does,
which I assume is why a lot of the flags are blown away... In any
event, I'm not sure how best to address this.

-bw

diff --git a/drivers/firmware/efi/libstub/Makefile
b/drivers/firmware/efi/libstub/Makefile
index 77a2b2d74f3f..945674048d8f 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -19,6 +19,14 @@ cflags-$(CONFIG_X86)         += -m$(BITS)
-D__KERNEL__ $(CC_FLAGS_DIALECT) \
                                   -fno-asynchronous-unwind-tables \
                                   $(CLANG_FLAGS)

+ifeq ($(CONFIG_X86_32)$(CONFIG_X86_64),y)
+ifdef CONFIG_CC_IS_CLANG
+ifdef CONFIG_CC_HAS_COUNTED_BY_PTR
+cflags-y                       += -fexperimental-late-parse-attributes
+endif
+endif
+endif
+
 # arm64 uses the full KBUILD_CFLAGS so it's necessary to explicitly
 # disable the stackleak plugin
 cflags-$(CONFIG_ARM64)         += -fpie $(DISABLE_KSTACK_ERASE) \